In the manufacture of sputtering targets used in the semi-conductor industry, it is desirable to produce a target with a sputter surface that will provide film uniformity and minimal particle generation during sputtering onto a semi-conductor wafer. The typical manufacturing processes for sputter targets result in targets with surface defects. Additionally, the materials comprising the sputter targets, such as titanium, aluminum, tantalum, nickel, chromium, cobalt and alloys thereof, have inherently problematic characteristics (i.e., particle size and uniformity and burn-in time requirements) that are a result of the machining process. These inherent defects and characteristics may have an adverse effect on the end user of the sputter target product.
Among the undesirable effects of sputter target manufacture is the lengthy bum-in time for a new sputter target at the customer site. Typically, sputter targets, such as titanium targets, exhibit poor film uniformity and high particle counts during the early stages of target use. As a result, a burn-in cycle, which eliminates the surface defects of the target, must be performed for as long as 30 kWh before the target surface will produce high quality thin film wafers. It is not uncommon for a standard target to go through about 50 wafers during the burn-in cycle before it produces high quality wafers, which is equivalent to about 6.7 kWh. Deposition without this burn-in cycle would result in a relatively high reject rate of poor quality wafers. Thus, the burn-in cycle is required to achieve a sputter surface that will provide the desired film uniformity and particle generation, but it requires a customer to waste valuable processing time and materials. By way of example, for titanium targets, 0.75-1.0% film uniformity is desirable, and 10 particles or less generated per 8 inch wafer is desired.
Various attempts have been made to reduce, eliminate or control the inherently undesirable characteristics resulting from the manufacturing process for sputter targets. For example, grinding, lapping, fine machining, lathes, and hand polishing have been used to remove the surface material of the target. These methods of material removal are time consuming, labor intensive, costly, dirty and provide inconsistent results. While polishing to a mirror finish may provide a good surface finish, it requires extensive preparation and time, usually 20-60 hours, which is unsuitable for a production environment, and there is no guarantee the same result may be obtained consistently for subsequent targets. Furthermore, sputter targets of marginal acceptability due to defects from unaccountable variances in manufacturing cannot be salvaged by the above techniques.
There is thus a need to provide a method for manufacturing sputter targets that provides a consistent finish with low particle counts and minimal surface defects, thereby reducing or eliminating burn-in time prior to use.